1. Field of the Invention
The invention is generally related to the area of optical communications. In particular, the invention is related to optical devices, modules or assemblies as pluggable devices processing light beams and the making thereof. The optical devices modules or assemblies include, but may not be limited to, 2-port pluggable fiber based WDM filters, pluggable optical fiber isolator, and miniature optical collimators.
2. The Background of Related Art
Optical fiber is an ideal waveguide than can transmit light between two ends thereof with very low loss to the light. However, a lot of optical functions available in free-space optics could be impractical or more expensive to be realized in the fiber media. For example, fiber collimators are widely used in fiber optic devices to couple light between fiber and free-space. As the characteristics of the light propagating in the fiber and in the free-space are usually very different, the interface between them are usually very lossy which makes a lot of applications impractical. With a collimator, one can achieve light coupling at low loss and a relatively long working distance in free-space to insert one or more free-space components in order to realize optical functions with complexity such as optical WDM, optical isolator, optical attenuator, and etc.
Currently, two types of collimators are widely used in telecom applications: C-lens collimators 100 and GRIN lens collimators 102 as demonstrated in FIG. 1 (a) and FIG. 1(b). Both approaches place a fiber facet at or around the focal point of a lens so that a light at the other side of the lens is collimated into paralleled beam to achieve a long working distance. Usually, a small angle (8°) is introduced at the interface between the fiber and the lens in order to manage the return loss to an acceptable level (usually 50-60 dB). As the C-lens and GRIN lens are both fabricated by bulk optical fabrication techniques, such as cutting, polishing and etc., it is difficult to achieve compact sizes (e.g., <1 mm). As the optical devices nowadays go smaller and smaller, which causes more and more complexities within the same dimension restrictions, these types of optical collimators of FIGS. 1 (a) and (b) limit the size of the optical devices.
Accordingly, there is a great need for such optical modules being made small, and at the same time, the collimators so designed are amenable to small footprint, broad operating wavelength range, enhanced impact performance, lower cost, and easier manufacturing process. Moreover, an emerging need for telecommunication devices calls for pluggable devices. Such needs have been witnessed by the active devices such as fiber optical transceivers and transponders that take a variety of form factors such as SFP, XFP, QSFP, CFP, etc. As the growth matures in active optical devices, passive optical devices such as optical WDM filters, multiplexers, attenuators, switches, isolators, will also need to match up to be pluggable in order to help more demand in planning and deployment flexibility. To facilitate such a pluggability need, fiber collimator dimension often is the limiting factor in order to shrink a fully functional passive device of interest to the necessary dimension.